Stationary engines, such as those used to drive generators (gensets), compressors, pumps and other applications are known. In certain applications, stationary engines utilize local fuel sources, for example, natural gas at a petroleum processing installation or hydrocarbon gases at landfills, for operation. The efficient use of gaseous fuel from the local source, which might have been wasted or otherwise disposed of, promotes the economical and environmentally friendly utilization of resources.
In most stationary engine applications using a local fuel as a source of energy, the supply of the local fuel is usually different from pipeline natural gas. As a result, for purposes of system design, the supply of fuel is presumed to be infinite and excess fuel is disposed of, for example, by burning in a flare stack.
Certain local fuel sources, however, require the expense of resources to produce a gas for use as a fuel. One such application involves use of a gasifier process in which a biomass of material, for example, wood chips generated at a lumber mill, are used to generate a combustible gas. Various gasifier processes are known, so the specific characteristics and types of such processes need not be described in detail herein. One common trait shared by most gasifier processes, whether they are high or low temperature applications, requires the consumption of the biomass material to produce the gas. When a gasifier process is used in conjunction with a genset or other stationary engine application, the oversupply of fuel produced by the gasifier process, which is intended to ensure a sufficient supply of fuel to the engine under all conditions, is wasteful.
Various solutions have been proposed in the past to increase the efficiency of gasifier processes used in conjunction with stationary engine applications. One such solution can be seen in expired U.S. Pat. No. 4,278,064 (the '064 patent), which is entitled “Fuel Control System for a Dual-Fueled Power Unit.” The '064 patent describes an engine coupled to a generator for electrical generation and adapted for dual fuel operation. The first fuel is diesel and the second fuel is producer gas generated in a down draft continuously operating producer of the moving-packed-bed vertical flow reactor type with co-current gas flow (see Abstract). As is described in the '064 patent, changes in electrical load of the generator cause changes to the load of the engine, which is manifested by undesired changes in engine speed during operation. The engine fueling is adjusted to compensate for engine speed changes such that the engine speed is maintained constant.